The invention generally relates to high frequency compression drivers and methods of manufacturing thereof. Such drivers are used for speaker systems calling for high quality sound reproduction at high volume as required in recording studios, theaters and the like.
A typical driver presently being marketed is composed of a base formed of magnetizable material having a centrally located upraised cylindrical portion. Surrounding this cylindrical magnetizable portion is an annular magnet having a central opening through which the cylindrical portion extends. An annular pole ring of magnetizable material also surrounds the cylindrical portion and is mounted upon the magnet. The cylindrical portion and pole ring serve as magnetic poles with the inner circumference of the pole ring being precisely spaced from the outer circumference of the cylindrical portion. A diaphragm having a downwardly extending cylindrical former around which a voice coil is wound is then mounted on the pole ring. Critical to the performance of the driver is the positioning of the voice coil between the spaced poles of the magnet. Thus, the circular voice coil must be precisely radially spaced between the inner circumference of the pole ring and the outer circumference of the cylindrical portion.
In prior devices, this voice coil centering has been accomplished by precisely machining the pole ring. For example, in one prior device, a circular indentation positioned radially outward from the central opening of the pole ring is precisely machined to receive the diaphragm. The diameter and concentricity of the indentation is predetermined to accurately radially space the voice coil from the inner circumference of the pole ring. The pole ring is then accurately mounted on the magnet to provide a predetermined distance between the inner circumference of the pole ring and the outer circumference of the cylindrical pole.
In another prior art device, the pole ring has a series of apertures arranged in a circle radially spaced from the inner circumference of the ring. These apertures are adapted to receive mounting posts upon which the diaphragm is mounted. By using these mounting posts, the voice coil is radially spaced a precise distance from the inner circumference of the pole ring. The pole ring, as in the other prior device, must then be precisely positioned with respect to the other cylindrical pole.
These prior devices suffer from a serious disadvantage that each pole ring in every device must be carefully machined which adds greatly to the cost of the device and is also a time-consuming process.
It is also extremely important, once the device is assembled, that the various elements not shift with respect to each other. Specifically, it is critical that the two pole members not shift with respect to each other, thereby destroying the proper positioning of the voice coil between them. In prior devices, the pole members and magnets are glued to each other. For example, the upper surface of the annular magnet is glued to the lower and adjacent surface of the pole ring. Maintaining the proper positioning of the pole ring therefore depends upon the shear strength of the glue. However, since a glue's shear strength is not nearly as great as its compression strength, the pole rings of such devices can be jarred into misalignment with respect to the voice coil and other pole member.
A typical diaphragm assembly used in prior devices consists of a circular disc having a centrally located dome-shaped diaphragm. The voice coil is attached to a cylindrical former which extends downward from the dome-shaped diaphragm. Extending upward from the outer circumference of the disc is a plastic rim which rests against the cover of the assembly. Thus, no portion of the surface area of the diaphragm is in contact with the cover. Such diaphragms have a tendency to overheat since they are not provided with a heat sink to dissipate heat energy which accumulates during the operation of the device. Moreover, such diaphragms assemblies are bulky and expensive to replace.
In prior devices, the diaphragm assembly typically includes electrical terminations on the upraised plastic rim. Wires extend from these terminations through apertures in the cover to exterior terminations on the cover. Typically, the covers are held against the diaphragm assembly through the use of screws. The number of electrical wires and terminations involved in prior devices increase the likelihood of electrical connection problems. Moreover, in order to gain access to the diaphragm, one must unscrew at least three or four screws which require a screw driver. Thus, in order to gain access to the magnet assembly and diaphragm, one must have room in order to use a screw driver and have freedom of hand manipulation. This is often not possible or convenient depending upon the location of the particular driver involved.
There is therefore a distinct need for a high frequency compression driver which can be manufactured simply and economically, and whose components can be easily replaced. In particular, there is a need for a method for centering the voice coil between the poles of the magnet without requiring expensive and time-consuming machining of the pole ring.
There is also a need for a diaphragm assembly which is easily replaceable and manufactured at low cost and which is provided with an adequate heat sink. Finally, there is a need for a device in which the elements of the magnet assembly are prevented from shifting with respect to each other after the voice coil has been properly aligned between the poles.